This invention generally relates to a valve closure device for maintaining a valve member in proper engagement with a valve seat. More particularly, this invention relates to a valve closure device that places a closing force directly onto a valve member adjacent a point of contact between the valve member and a mating valve seat.
A variety of wafer or butterfly-type valve arrangements are known that include a valve member or disk that pivots, relative to a valve seat, between an open and closed position. One application for such valve assemblies is in regenerative incinerators. Strict governmental regulations require that gas leakage through such valves be minimized to reduce pollutants expelled into the atmosphere. Accordingly, several attempts have been made at improving the efficiency of such valves.
These valves typically include a valve disk that rotates about a shaft between a closed position, where the valve disk mates with a valve seat, and an open position. Prior attempts at improving the seal at the disk/valve seat interface include increasing the torque applied in a closing direction to the shaft. The increased torque has not proved satisfactory because the torque, which is applied to the rotating shaft, does not reach the edges of the valve disk, which contact the valve seat. As one example, in regenerative incinerators, the valve disks are subjected to relatively high differential pressures that cause the disk to deflect away from the valve seat. In the past, this may have resulted in undesirable leakage through the valve.
Another attempt at overcoming the difficulties associated with conventional valve assemblies has been to add soft, resilient seals to mate the valve disk with the seat. A significant disadvantage associated with this attempt is that the high temperatures, extreme cycling and contaminated air streams in regenerative incinerators harden the resilient seals. The seals then abraid, resulting in greater leakage than experienced in a system having no such seals.
It is also known to use weights to close a disk valve assembly. The known weight systems, however, suffer from the drawback that the weights are typically mounted away from the disk on a cantilever arm that extends from one or both sides of the disk shaft. Accordingly, any torque imparted by the weights is applied to the disk shaft, which is insufficient for maintaining a closing force at the disk edges. Further, known weight systems are relatively cumbersome and mounted outside of the flow passageway, which further reduces the amount of torque imparted to the disk edges. Moreover, having additional weights on the exterior cambers or bends the disk shaft, which potentially compromises the ability to mate the disk with the valve seat and causes more undesirable leakage.
This invention provides a valve closure device that overcomes the drawbacks and shortcomings of the prior art described above. A valve closure device designed according to this invention operates within the flow passageway to impart a closing force directly adjacent the edges of the valve disk, where it is most needed.